Henrik Lehrmann Christiansen

Cloud RAN for Mobile Networks—A Technology Overview

Cloud Radio Access Network (C-RAN) is a novel mobile network architecture which can address a number of challenges the operators face while trying to support growing end-users needs. The main idea behind C-RAN is to pool the Baseband Units (BBUs) from multiple base stations into centralized BBU Pool for statistical multiplexing gain, while shifting the burden to the high-speed wireline transmission of In-phase and Quadrature (IQ) data. C-RAN enables energy efficient network operation and possible cost savings on baseband resources. Furthermore, it improves network capacity by performing load balancing and cooperative processing of signals originating from several base stations. This paper surveys the state-of-the-art literature on C-RAN. It can serve as a starting point for anyone willing to understand C-RAN architecture and advance the research on C-RAN.

Novel scheme for packet forwarding without header modifications in optical networks

We present a novel scheme for packet forwarding in optical packet-switched networks and we further demonstrate its good scalability through simulations. The scheme requires neither header modification nor any label distribution protocol, thus reducing component cost while simplifying network management.

Optimal assignment of cells in C-RAN deployments with multiple BBU pools

Cloud Radio Access Network (C-RAN) is receiving increasing attention not only within the research community but also from operators and standardization bodies. However, even a good technology will be deployed only if it is economically viable. In our previous work, for larger scale deployment we recommend to divide the area into multiple BBU Pools. In this paper we show how to optimally assign cells to different BBU Pools in such a scenario. By using Integer Linear Programming (ILP) method we derive engineering guidelines for minimizing the CAPital EXpenditure (CAPEX) of C-RAN deployment.

Synchronization challenges in packet-based Cloud-RAN fronthaul for mobile networks

In this paper, we look at reusing existing packet-based network (e.g. Ethernet) to possibly decrease deployment costs of fronthaul Cloud Radio Access Network (C-RAN) network and cost of Baseband Unit (BBU) resources. The challenge of this solution is that it requires mobile traffic (until now transmitted over synchronous protocols) to traverse the asynchronous Ethernet without losing synchronization. We analyze synchronization requirements of mobile networks and present an overview of solutions that fulfill them in traditional mobile networks. Then we elaborate on challenges that packet-based fronthaul imposes. We analyze possible contributions to frequency and phase error. We verify the feasibility of using the IEEE 1588v2 also know as Precision Time Protocol (PTP) for providing accurate phase and frequency synchronization. The study is based on simulations made in OPNET modeler. Thereby we bridge the gap between Ethernet and mobile network domains creating a comprehensive architectural analysis.

Cloudification of mmwave-based and packet-based fronthaul for future heterogeneous mobile networks

Current deployments of mobile networks are seriously challenged by increasing capacity demands, and traditional solutions are no longer practical. The use of small cells is considered as a viable technique to meet these demands. In this context, the use of centralized signal processing in a pool is seen as an enabler for next-generation heterogeneous mobile networks. This allows for simpler base stations and savings in deployment costs, but introduces challenges in the fronthaul network connecting the sites to the processing pool. The fronthaul needs to have very low latency and high capacity, but the traditional architecture of this network uses point-to-point links between each site and the pool, thus making it impossible to share capacity as the demands change. To address these challenges, a flexible network architecture for the fronthaul is presented that is based on Ethernet to carry the baseband samples. This architecture is integrated with baseband over millimeter waves for the fronthaul toward the small cells to save in fiber deployment and cope with the spectrum shortage in the traditional microwave frequencies. Simulation results show that few hundreds of microseconds of latency in the fronthaul can be tolerated for the applications running in the user equipment to respond within acceptable times. Furthermore, our estimations show that the use of millimeter waves allows an 11 percent reduction in the number of cells needed for the same traffic volume.

Performance of Non-Orthogonal Multiple Access (NOMA) in mmWave wireless communications for 5G networks

Among the key technologies that have been identified as capacity boosters for fifth generation - 5G - mobile networks, are millimeter wave (mmWave) transmissions and non-orthogonal multiple access (NOMA). The large amount of spectrum available at mmWave frequencies combined with a more effective use of available resources, helps improving the overall capacity. NOMA, unlike orthogonal multiple access (OMA) methods, allows sharing the same frequency resources at the same time, by implementing adaptive power allocation. In this paper we present a performance analysis of NOMA in mmWave cells, using OMA as a benchmark. The results show that up to 70% channel capacity gain can be achieved when using NOMA instead of OMA. Most of the NOMA studies to the date focus mainly on the capacity gain; therefore we also present an analysis of the required signal-to-interference-plus-noise ratio (SINR) in NOMA, needed to achieve a target block error rate (BLER). The results show that an average SINR penalty of 12 dB is present when choosing NOMA over OMA.

Fronthaul dimensioning in C-RAN with web traffic for coordinated multipoint joint transmission

The use of centralized signal processing for dense urban mobile networks is gaining interest both in research and in industry. Gathering most of the base station functionalities in a processing pool would enable capacity sharing and the implementation of advanced techniques such as coordinated multi-point. Nevertheless, this puts stringent requirements on the network interconnecting the processing pool and the sites, especially in terms of maximum latency. In this paper, we provide results for dimensioning the fronthaul network that are obtained through modelling and discrete-event simulation. We model the full protocol stack for the network end-to-end in order to use realistic application-layer traffic and user behavior models. Our results show that the fronthaul latency should be kept below 0.6 ms in order to ensure optimal performances for the application.

Optimizing Cloud-RAN deployments in real-life scenarios using Microwave Radio

Cloud Radio Access Network (C-RAN) is a new architecture designed to be the candidate for enabling future mobile networks. However, it will be deployed only if it is economically viable. In this paper we investigate the technological options of C-RAN deployments. By using analytical methods we derive engineering guidelines for minimizing the CAPital EXpenditure (CAPEX) of C-RAN deployment. We show for which population density and span of BBU Pool coverage usage of Microwave Radio (MWR) links is viable. For larger scale deployment we recommend to divide the area into multiple BBU Pools.

A framework for joint optical-wireless resource management in multi-RAT, heterogeneous mobile networks

Mobile networks are constantly evolving: new Radio Access Technologies (RATs) are being introduced, and backhaul architectures like Cloud-RAN (C-RAN) and distributed base stations are being proposed. Furthermore, small cells are being deployed to enhance network capacity. The end-users wish to be always connected to a high-quality service (high bit rates, low latency), thus causing a very complex network control task from an operators point of view. We thus propose a framework allowing joint overall network resource management. This scheme covers different types of network heterogeneity (multi-RAT, multi-layer, multi-architecture) by introducing a novel, hierarchical approach to network resource management. Self-Organizing Networks (SON) and cognitive network behaviors are covered as well as more traditional mobile network features. The framework is applicable to all phases of network operation like planning, deployment, operation, maintenance and therefore aids network operators in improving their business potential.

Macro Cell Assisted Cell Discovery Method for 5G Mobile Networks

The use of millimeter wave (mmWave) frequencies in next generation mobile networks - 5G networks -, is now a fact. mmWave allow to overcome the spectrum scarcity in microwave frequencies and supply the demanded capacity Nevertheless, the use of these frequencies comes with challenges to the network, and requires a new system design. The aspects concerning the impact of using mmWave frequencies on the medium access (MAC) layer are one of the topics that need to be further analyzed. In this article we focus on the cell discovery process of the MAC laywe for mmWave communications. A new approach assuming a joint search of the user equipment (UE) between the mmWave small cell (SC) and the macro cell (MC) is proposed. The performance of this method is analyzed and compared with existing methods. The results show that using the MC as aid during the search process can allow for up to 99% improvement in terms of attempts needed to find the UE.